1. Field of the Invention
The present invention relates generally to photographing devices, and more particularly, to a lens module.
2. Description of the Related Art
As the digital products have been diversified, such as personal digital assistants (PDA), mobile phones, or other small portable terminal apparatuses, each of them is broadly combined with a miniature photographing device, like lens module, to have photographing function. In the early application to such digital products, the lens modules are mostly formed of fixed-focus lenses which fail to adjust the local length and then to vividly photograph landscape at short range.
To provide the consumers with better photographic quality, the manufacturer developed a miniature lens module for adjustment of local length. FIG. 1 illustrates a focusing miniature lens module, which is composed of a base A1, a focusing ring A2, a holding member A3, and a lens barrel A4. The focusing ring A2 includes a plurality of recessions A21 formed at an internal sidewall thereof. Each of the recessions A21 has at least two positioning portions A22a and A22b and an inclined portion A23. The positioning portions A22a and A22b are formed at a bottom side of the focusing ring A2 and located axially at different positions of the same. The inclined portion A23 is located between the two positioning portions A22a and A22b. The focusing ring A2 further includes a plurality of lugs A24 formed on an external edge thereof. The base A1 includes an upright annular wall A11, and a plurality of convex portions A12 protruding outward from an external edge thereof and corresponding to the recessions A21 and having the same number as the recessions A21. The focusing ring A2 is fitted onto the upright annular wall A11 of the base A1 to enable the positioning portions A22a to lie against the corresponding convex portions A12. The holding member A3 is mounted onto the base A1, having a plurality of holding tongues A31 corresponding to the lugs A24 respectively and holding the corresponding lugs A24 for enabling the positioning portions A22a to closely lie against the corresponding convex portions A12. The lens barrel A4 is mounted onto the focusing ring A2 for receiving a set of lenses.
In light of the above, when the focusing ring A2 is rotated on the upright annular wall A11, the focusing ring A2 lies against the convex portions A12 and then moves along the inclined portion A23 from the positioning portion A22a to the other positioning portion A22b. Because the two positioning portions A22a and A22b of each recession A21 are located axially at different positions of the focusing ring A2, when the focusing ring A2 lies against the convex portions A12 and then moves along the inclined portion A23 from the positioning portion A22a to the other positioning portion A22b, the axial distance between the focusing ring A2 and the base A1 is subject to change for adjustment of the local length.
The aforementioned lens module A is defective in that the concentricity between the lens set in the lens barrel A4 and the image sensor B is subject to deviation, because the lens barrel A4 mounted onto the focusing ring A2 is subject to rotation along with the focusing ring A2 while rotated, to depart the focus spot of the lens set from the image sensor B where images ought to be received, further affecting the imaging quality.